Alterations of cell shape are an important component of many fundamental cell processes including movement, division, and differentiation. Medically important shape changes include those undergone by platelets during blood clotting and those exhibited by neutrophils and macrophages during phagocytosis. The molecular basis for these shape changes lies in the reorganization of cell's cytoskeletal proteins, chiefly the structural proteins actin and tubulin. The organization state of these two major cytoskeletal elements is in turn regulated by a host of actin binding and microtubule associated proteins (MAP). Explaining the molecular basis of cell shape changes is dependent on the understanding of the in vivo function of ABPs and MAPs. One excellent model experimental system for examining the functions of ABPs and MAPs is the sea urchin coelomocyte. These primitive blood cells can be considered as a cross between the vertebrate platelet and macrophage in that they change shape during coelomic fluid coagulation, are highly phagocytic and can be motile. Coelomocytes can be induced to undergo synchronous, actin mediated shape changes from a lamellipodial to a filopodial form as well as the reverse. This proposal describes a series of morphological and biochemical experiments aimed at the identification of coelomocyte ABPs and MAPs and the elucidation of their in vivo functions during shape changes. ABPs and MAPs will be identified from actin and tubulin binding overlays of blots of cell extracts, from taxol stabilized microtubule preparations and from DNase affinity chromatography. Immunolocalization at the light and electron microscopic levels will be used to examine the distribution of ABPs and MAPs in coelomocytes with particular emphasis on the filopodial to lamellipodial shape change. This allows for the examination of the dismantling of the actin cytoskeleton and the function of MAP motor proteins in the distribution of cellular organelles.As a secondary aim, the calcium regulation of coelomocyte shape changes will also be investigated using experiments employing calcium ionophore treatments and calcium dependent fluorescent dyes. The results of these experiments should provide new insights into the identity and functions of ABPs and MAPs in coelomocyte shape changes and should also help lead to a better understanding of the medically significant shape changes exhibited by platelets and macrophages.